Elk uses 2.2K EOL resistors on all zones, with the exception of a 2-wire smoke zone. These are the resistors that come with the M1 and are marked with 3 red bands. Only one EOL resistor is used per zone, no matter whether you have 1, 2, 3, 4 or any other number of contacts wired up to form the zone. Note that you don't have to use EOL resistors on burglar zones if you don't want to. You can configure them on a zone by zone basis. They provide better supervision of the zone, but require extra work to install them.
Below is a diagram of how to wire multiple 4-wire smokes in a proper daisy chain. Note how the "+" wire uses 2 terminals on each detector. Be sure to connect the wires using both screws. Don't just loop it through one screw, or use a pig tail. Connect one wire to each screw.
There are two Elk 2.2k EOL resistors required on the COSMOD4W itself. Then you also need a System Sensor 3.9k EOL resistor goes at the end of the daisy chain along with the EOLR-1 relay. This resistor should come with the COSMOD4W. There is just the one EOL relay, and it gets connected to the last smoke detector in the chain. That way, it monitors that power is making it all the way to the end of the chain. If there is power at the last smoke detector, then that's a good indication that all the other smoke detectors are also receiving power.
You'll need 2 Elk 924 relays to trigger the smoke and CO inputs on the COSMOD4W.
Have you done a current draw calculation on your system to see if you might need an aux power supply? The 3 smokes plus the COSMOD4W require 195 mA max (combined) in alarm condition, plus another 60mA for each of the relays (120mA total). The M1 can provide up to 1.0A of power, so whether or not you need an aux power supply will depend on what else the panel is powering, such as keypads, M1XEP, zone expanders, motion detectors, etc. The numbers can add up pretty fast.
Elk has a
current draw spreadsheet to help make this simple.
The battery that came with the M1 is the back up battery for the M1's power supply. If you have an aux supply, it would have its own battery.